My point is simple.
How would Toriko deal with a swarm of Gourmet World beasts (lets say, a swarm of about 60 of them) with a capture level of around, lets say, 110, while being in some very heavy gravity or some other crazy environment, if he barely managed to beat a single beast with a capture level of 140, one on one, in a normal environment?
The scenario I described is a more than likely scenario since thats basically what happened to Toriko when he tried to go to the Gourmet World, and I don't see how he would be able to get out of a situation like that, which would be a standard situation in Gourmet World, without being in risk of losing his life.
Basically, I don't see how I can consider Toriko ready for Gourmet World if even a standard, more than likely situation for Gourmet World seems to be very dangerous for Toriko. And if he barely managed to beat a beast of 140 in capture level one on one in the human world, I would still consider a standard situation like that very dangerous for Toriko.
In short, the fight against the 4 beast's limb showed us how strong and awesome Toriko has become by being able to defeat a beast like that with a few of his strong attacks (he had to use leg knife, one of his strongest techniques) and also without putting himself in danger (that trait will be important to survive Gourmet World), which I think is necessary for us to feel that a standard situation in Gourmet World, similar to the one he faced in the past, would no longer actually be life threatening for him, meaning that he is able to move to Gourmet World and start to discover its secrets. And its the same for the other Kings.
Btw, its interesting that you mentioned Luffy since One Piece actually did something similar to this. After the timeskip, Luffy quickly destroyed a pacifista like the ones from the war that were giving so much trouble even to new world pirates. He did it with a strong attack and without letting himself be in danger. That scene basically told us: "Look, now Luffy can deal with enemies like these, that could even give new world pirates trouble, quickly and even without it being life threatening for him at all, which means that he is ready for New World!"
That is pretty much what happened in Toriko. The only difference is that the enemy wasn't one from the past. But it was an enemy capable of giving trouble to the other beasts in gourmet world, like the pacifista was an enemy capable of giving new world pirates trouble.